An improved description of clathrate hydrates using classical density functional theory coupled with a simple lattice gas and van der Waals-Platteeuw theory

The present study refines a recently published model which described clathrate hydrate phase equilibria by coupling the statistical mechanical van der Waals-Platteeuw approach with a mean-field lattice gas in the framework of classical density functional theory. This model yielded analytical expressions for the cavity occupancy, and requires, in principle, knowledge of only two parameters: The potential energy well depth, and a hard-sphere radius for the gas-water interaction. The present contribution expands on this model by examining the utility of several modifications in order to improve its accuracy in describing the dissociation pressure curves of a dozen clathrate hydrates: Argon, carbon dioxide, carbon monoxide, ethane, ethene, hydrogen sulphide, krypton, methane, nitrogen, propane, sulphur dioxide, and 1,1,1,2-tetrafluoroethane. A modified model is demonstrated which produced a good fit to experimental data for the 12 gas hydrate systems considered in this study, with an absolute average temperature deviation of less than 0.7% in all cases.